Method for Manufacturing Optical Devices

ABSTRACT

A method for manufacturing an optical device including at least one silicone elastomer optical waveguide includes the steps of providing a substantially rigid mold with a patterned surface, providing a core layer of a curable silicone elastomer, patterning the core layer by means of the patterned surface of the substantially rigid mold, curing the patterned core layer, and removing the substantially rigid mold from the patterned core layer. The method advantageously allows the manufacture of an optical device including at least one optical waveguide in a single step and in a reproducible manner.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing opticaldevices. Specifically, the invention relates to a method formanufacturing optical devices comprising silicone elastomer opticalwaveguides of improved quality in terms of dimensional and shapeprecision, as well as in terms of low optical loss.

PRIOR ART

In optical communication systems, messages are transmitted by carrierwaves at optical frequencies which are generated by sources such aslasers and light-emitting diodes. There is interest in such opticalcommunication systems because they offer several advantages overconventional communication systems.

One means for switching or guiding waves of optical frequencies from onepoint to another is by an optical waveguide. The operation of an opticalwaveguide, in particular, is based on the fact that when alight-transmissive medium (known in the art as “core”) is surrounded orotherwise bounded by at least another medium having a lower refractiveindex (known in the art as “cladding”), the light introduced along thecore axis is reflected at the boundary with the surrounding medium, thusproducing a guiding effect.

A wide variety of optical devices can be made which incorporate a lightguiding structure as the light transmissive elements. Such devicescomprise, for example, components such as channel optical waveguides,ridge, raised strip, embedded strip, diffused, rib and inverted ribwaveguides, optical couplers, optical splitters, optical switches,optical filters, variable attenuators, micro-optical elements and thelike, as from U.S. Pat. No. 6,555,288, for example.

Typically, an optical waveguide comprises:

-   -   a support,    -   a lower cladding layer formed on the support (the lower cladding        layer being optional, depending on the value of the refractive        index of the support),    -   a core layer formed on the lower cladding layer (if present) or        on the support (if this has a refractive index lower than the        refractive index of the core), the core layer being provided        with a rib portion integral with the core layer, and    -   an upper cladding layer formed on the core layer.

Optical waveguides and other optical devices comprising a core and/orcladding layer(s) made of elastomeric materials, such as silicones, areknown. The waveguides made of elastomeric materials are heat andmoisture resistance, have low loss at 1550 nm wavelength, which is thewavelength commonly used in telecommunication applications, have lowbirefringence and high thermo-optic coefficient (dn/dT).

As is well known in this art, birefringence is the difference betweenthe refractive index of the transverse electric or TE polarization(parallel to the support surface) and the transverse magnetic or TMpolarization (perpendicular to the support surface). Such birefringenceis undesirable in that it can cause optical devices to show substantialpolarization dependant losses and increased bit error rates intelecommunication systems.

A first known method for manufacturing an elastomeric optical waveguideis based on the so-called photolithography process, which is carried outover a layer of elastomeric material, as reported, for example, by U.S.Pat. No. 6,084,050 and U.S. Pat. No. 5,972,516. Both such documentsrefer to optical waveguides made of materials comprising siloxane bonds(—Si—O—Si—) in the main chain.

Photolithography is a traditional process involving selective exposurethrough an appropriate mask of a light-sensitive polymeric layerdeposited on the core layer, in order to develop a pattern. Developmentmay be accomplished, for example, by removal of the unexposed portion ofthe photopolymeric layer by an appropriate solvent and then by differentsteps of reactive ion etching (R.I.E.) on the core layer.

A method based on such a process is however quite long and expensive, inthat it involves a series of complex steps, namely those of masking andof reactive ion etching the layer made of elastomeric material.Furthermore, the reactive ion etching (R.I.E.) of an elastomericmaterial such as a material comprising a siloxane bond can bringdrawbacks: the gas employed in the etching process can either form apassivating layer (e.g. SiO₂, as can be observed if oxygen is used) orcan show to be not sufficiently selective in the sense that the etchingis not limited to the elastomeric layer, but may affect also a possibleunderlying layer (as can be observed if a blend of fluorinated andchlorinated gases is used).

Furthermore, the Applicant observed that the siloxane optical devicesobtained by manufacturing methods including a R.I.E. step can havesurface defects which lead to propagation loss.

The Applicant perceived that the optical losses in optical devices madeof siloxane materials can be due to the fact that R.I.E. can yieldroughness of the core surface, and this may result in unacceptablescattering losses.

EP-A-1 118 884 discloses another method for manufacturing an opticalwaveguide, namely by molding an organopolysiloxane material obtained bymeans of a sol-gel process. More particularly, EP-A-1 118 884 disclosesa method for manufacturing optical waveguides made ofpolyorganosiloxanes formed by selecting raw materials for a sol-gelmaterial which provide a dimethylsiloxane and a phenylsiloxane throughhydrolytic and dehydration/condensation reactions. In order tomanufacture an optical element covered with a film having a surfacewhich is the inversion of the surface of a mold, EP-A-1 118 884 providesa process comprising the steps of pouring a sol-gel material over thesurface of the substrate, a first heating to carry out adehydration/polycondensation, pressing the mold against the film on thesurface of an article when the liquid film achieves plasticity, a secondheating in this state to almost complete thedehydration/polycondensation reaction of the sol-gel material forgelation, transfer molding, releasing the mold, and a third and finalheating of the film to completely polycondense the film and vaporizewater formed by this polycondensation.

Firstly, as a consequence of the application of such a process, in orderto promote the dehydration/polycondensation reaction, three distinctheating steps are carried out, which result in a shrinkage of theelastomeric film and in an ensuing cracking of the elastomeric film.

Secondly, residual hydroxyl groups can be present in the resultingmaterial, which yields an unacceptable loss at a wavelength of 1550 nm.

Thirdly, the elastomeric film so obtained has an uncontrolled porosity,which can provide an unpredictable refractive index and scatteringlosses.

SUMMARY OF THE INVENTION

The Applicant observed that although silicone elastomer materials areheat and moisture resistant, have low loss at 1550 nm wavelength, havelow birefringence and high thermo-optic coefficient, the manufacturingmethods of the prior art intended to manufacture optical devices made ofsuch elastomeric materials are unsatisfactory in that, on the one side,they comprise a number of steps making such known methods too complexand time-consuming, and in that, on the other side, the optical devicesmanufactured by such methods can show unacceptable optical loss due to apoor dimensional precision.

In particular, the Applicant has observed that the complexity of themanufacturing methods of the prior art show drawbacks that can hold backfrom using silicone elastomers despite the advantageous properties ofsuch materials.

Accordingly, the Applicant perceived the need of devising a new methodfor manufacturing silicone elastomer optical devices, for examplesilicone optical waveguides, provided with a predetermined pattern, inparticular but not exclusively of the rib and inverted rib type, whichallows to manufacture such devices with a reduced number of steps, whileensuring to obtain a dimensional precision such to maintain or enhancethe optical properties, especially in terms of reduced optical losses,which are intrinsic of silicone elastomer materials.

In this regard, the Applicant observed that in order to obtain siliconeelastomer optical devices in a reduced number of steps, the veryproperties of silicone elastomer materials, and particularly theelasticity and the low adhesion to other materials, may be convenientlyexploited.

The Applicant observed that a silicone elastomer optical device can beobtained by molding a layer of a curable silicone elastomer with apatterned substantially rigid mold. By molding a layer of a curableelastomeric material with a substantially rigid mold having apredetermined patterned surface, it is advantageously possible toprovide the elastomeric layer with a corresponding resulting patternwhich is the negative of the pattern of the mold, such resulting patternhaving a neat shape. Furthermore, a substantially rigid mold, preferablybut not exclusively made of a polymer, can be advantageously used morethan once without loss of the desired reproducibility and without anydamage because silicone elastomers show a low adhesion to a very broadrange of materials adapted to form a mold.

The present invention, therefore, relates to a method for manufacturingan optical device comprising at least one silicone elastomer opticalwaveguide, said method comprising the steps of:

-   -   providing a substantially rigid mold with a patterned surface;    -   providing a core layer made of a curable silicone elastomer;    -   patterning said core layer by means of the patterned surface of        the substantially rigid mold;    -   curing the patterned core layer; and    -   removing said substantially rigid mold from said patterned core        layer.

For the purpose of the present description and of the claims whichfollow, except where otherwise indicated, all numbers expressingamounts, quantities, percentages, and so forth, are to be understood asbeing modified in all instances by the term “about”. Also, all rangesinclude any combination of the maximum and minimum points disclosed andinclude any intermediate ranges therein, which may or may not bespecifically enumerated herein.

Thanks to the fact that the core layer is made of a curable siliconeelastomer, and that the patterning step is effected by a patternedsurface of a substantially rigid mold, it is advantageously possible toobtain an elastomeric device in a single step.

In particular, differently from the prior art manufacturing method basedon a sol-gel process, which requires a number of heating steps to carryout the dehydration/polycondensation, the method of the presentinvention can comprise a single heating step or none at all. Inparticular, a single heating step is provided in case the curing step isa thermal curing, while no heating step is necessary if the curing stepis a photocuring, for example a UV curing step.

Furthermore, thanks to the fact that silicone elastomers show a lowadhesion to a very broad range of materials adapted to form a mold, suchas, as described in more detail in the following, polymers, fluorinatedpolymers, but also inorganic materials, the material intended to formthe mold may be selected within a broad range of materials.

Because of such low adhesion of silicone elastomers, the mold can beadvantageously used more than once, while achieving the desiredreproducibility of the predetermined pattern, thus ensuring adimensional and shape precision of the pattern reproduced on the corelayer, as well as an improved surface smoothness.

Furthermore, since to cure the materials used in this inventiondehydration/condensation reactions like in sol-gel process are notrequired, substantially no hydroxyl groups are present in the corelayer, with advantageous attainment of improved transmission capabilityat a wavelength of 1550 nm of the optical device manufactured accordingto the invention.

According to a preferred embodiment of the method of the invention, thecore layer has an initial volume and the cured patterned core layer hasa final volume which is substantially equal to said initial volume.

In the present description and in the claims, the final volume isintended to be substantially equal to the initial volume if no volumeshrinkage of the cured core layer is observed with respect to the volumeof the core layer measurable before the curing step or, at the maximum,a volume shrinkage of 5%.

Preferably, the above-mentioned final volume of the core layer after thecuring step is 95-100% of the initial volume of the core layer beforethe curing step.

Preferably, the core layer is made of a thermally curable siliconeelastomer.

An example of curable silicone material is polydimethylsyloxane (PDMS).A preferred alternative of curable silicone elastomer is apolyphenylmethylsyloxane (PPMS). If the curable silicone elastomer is aPPMS, the ratio of methyl and phenyl groups can be advantageously usedto control and modulate optical properties of the material, likerefractive index and optical loss.

Alternatively, the core layer is made of a UV curable siliconeelastomer. For example, it can contain photocurable functional groupslike acrylates. In such preferred embodiment, the mold is preferablymade of a substantially rigid material transparent to UV light, so thatthe curing step of the patterned core layer may precede the removingstep of the method of the invention.

According to a preferred embodiment of the method of the invention, thepatterned surface of the mold, for example intended to form the ribs ofan elastomeric optical waveguide, shows recesses in the mold.Advantageously, in such manner a rib optical waveguide may be produced.

Alternatively, the patterned surface of the mold shows projectionsprotruding from the mold. Advantageously, in such manner an inverted riboptical waveguide may be produced.

Although the present description is mainly focused upon the manufactureof rib waveguides, the method according to the present invention may becarried out to manufacture any optical device. In particular, the methodmay be carried Out to manufacture, for example, optical components suchas rib and inverted rib waveguides, optical couplers, optical splitters,optical switches, optical filters, variable attenuators, micro-opticalelements and the like.

Preferably, the mold is made of a polymeric material.

Polymeric materials can also be easily processed and show excellentmechanical properties.

Preferably, the polymeric material is curable and, more preferably,photocurable, for example UV curable.

Alternatively, the mold can be made of a thermoplastic polymericmaterial.

A curable polymeric mold may be advantageously manufactured byconventional techniques, e.g. by pouring a polymeric material in liquidform on a master provided with recesses and/or protrusions correspondingto the ribs of the optical device to be produced. A sheet is preferablyleant on the uncured polymeric material in order to obtain a solidsupport for the mold, which can be made of an inorganic material, suchas glass. Finally the polymeric material is cured.

Alternatively, a polymeric mold may be advantageously manufactured byinjection molding, by a conventional photolithographic process or by animprinting technique, such as hot embossing or UV imprintinglithography.

According to a preferred embodiment of the method of the invention, themold is made of a fluorinated polymeric material.

By suitably selecting the substantially rigid material constituting themold within such preferred class of materials, an improved releasabilityof the mold from the core layer may be advantageously achieved. As aresult, a further advantage is achieved, namely that the mold may bere-used a high number of times, which allows to manufacture an opticaldevice at minimized manufacturing costs.

Preferably, the fluorinated polymeric material of which the mold is madeis selected from fluorinated acrylate and methacrylate polymers,fluorinated polyacetates, fluorinated polyesters, fluorinatedpolystyrene, PVDF, fluorinated polycarbonates, fluorinated polyimides,fluorinated polyethyleneterephtalates (PET), fluorinatedpolycyclobutanes, fluorinated polycyanates, or combination thereof.

The fluorinated acrylate and methacrylate polymers are preferablyselected from fluorinated polymethylmethacrylate, fluorinatedpolybutylacrylate, fluorinated polyethylexylacrylate, fluorinatedpolyisodecylacrylate, fluorinated polyhydroxyethylacrylate, fluorinatedpolyhydroxypropylacrylate, fluorinated poycycloexylacrylate, fluorinatedpolybutane-dioldiacrylate, fluorinated polydiacrylate, fluorinatedpolyneopentylglycoldiacrylate, fluorinatedpolydiethyleneglycoldiacrylate, fluorinatedpolydiethyleneglycoldimethacrylate, fluorinatedpolyexyanedioldiacrylate.

According to an alternative embodiment of the method of the invention,the mold is made of an inorganic material which can be advantageouslymanufactured by a conventional technique, e.g. by a photolithographicprocess or by an imprinting technique.

The mold is preferably made of an inorganic material selected from: Si,Cr, Ni, Pt, Ti.

A silicon mold may be advantageously patterned by a conventionalphotolithographic technique comprising resist deposition, UV irradiationthrough a mask, Reactive Ion Etching.

A metal mold, for example made of one of the preferred metals indicatedabove, may be advantageously manufactured by a conventional techniquesuch as electroplating or sputtering.

When the mold is made of an inorganic material such as one of thepreferred inorganic materials described above, the preferred embodimentof the method of the invention further comprises the step of applying areleasing agent on the patterned surface of the mold before theabove-mentioned step of patterning the core layer.

In this way, an enhanced releasability of the mold from the core layermay be advantageously achieved.

As an illustrative example, the releasing agent may behexamethyldisilazane (HMDS). Alternatively, the releasing agent may be afluorine based releasing agent (e.g. Daifree® compounds by DaikinIndustries Ltd.)

The core layer can be provided either in direct contact with a supportor arranged on a support previously provided with a lower cladding layerof a predetermined material having a refractive index lower than therefractive index of the core layer. In the latter case, theabove-mentioned predetermined material is thus in contact with theelastomeric material of the core layer.

If present, the lower cladding layer is preferably of a firstelastomeric material, which is thus in contact with the elastomericmaterial of the core layer.

The core layer and the optional lower cladding layer can be provided onthe support in liquid form by different methods known in the art, suchas spin coating, dip coating, slot coating, roller coating, doctorblading, liquid casting or the like.

The support can be made of any material suitable to perform a supportaction for the elastomeric material to be patterned by means of thesubstantially rigid mold.

Advantageously, the support is made of a material provided with heatresistance, mechanical strength, elastic modulus and chemicalresistance. Examples of material suitable for the support arepolyetherimide, polyimide, polycarbonate, polyurethane, quartz andglass.

In order to improve the adhesion of the core layer and of the optionallower cladding layer to the support, the latter may be preliminarycleaned and treated with an adhesion promoter. The support may containother devices, either topographical features such as grooves orelectrical circuits, or electro-optical devices such as laser diodes.

When the core layer is provided in direct contact with the support, thelatter is made of a material with a refractive index lower than that ofthe silicone elastomer of the core layer.

When the support is provided with a lower cladding layer, the refractiveindex of the Support material becomes irrelevant to the operation of theoptical device.

The first elastomeric material has a refractive index lower than that ofthe elastomeric material. Preferably, said first elastomeric material isa material selected, for example, from the group mentioned above inconnection with the elastomeric material of the core layer.

The first elastomeric material is preferably a curable silicone materialhaving a lower refractive index than the refractive index of the corelayer.

Preferably, the first elastomeric material is a polysyloxane having alower refractive index than the refractive index of the core layer.

Preferably, the first elastomeric material is a polyphenylmethylsyloxane(PPMS) having a lower refractive index than the refractive index of thecore layer.

Another illustrative example of elastomeric material adapted to form alower cladding layer is polydimethylsyloxane (PDMS).

When the first elastomeric material is a curable material provided onthe support in liquid form, a curing treatment thereof is preferablyeffected before providing the core layer thereupon. For example, thefirst elastomeric material can be cured by thermal treatment or byactinic radiation, for example UV radiation.

Alternatively, the first elastomeric material is cured after beingprovided on the support.

Advantageously, the UV curing is effected substantially in the absenceof oxygen, for example under a nitrogen flow.

The thermal curing conditions can be determined by the skilled in theart on the basis of the product sheet of the first elastomeric material(e.g. for a period of time of 1 h at a temperature of 100° C., for aperiod of time of 4 h at a temperature of 65° C.).

The curing step of the patterned core layer may precede or follow theremoving step of the method of the invention.

The curing of the core layer is preferably effected by thermal treatmentor, alternatively, by actinic radiation, for example UV radiation.Preferably, such UV curing is effected substantially in the absence ofoxygen, for example under a nitrogen flow.

The thermal curing is for example effected at a temperature of 150° C.for a period of time of 2 h, or for a longer time at a lowertemperature.

Preferably, the method of the present invention further comprises thestep of providing an upper cladding layer of a second material,preferably a second elastomeric material, on the core layer, after thestep of removing the substantially rigid mold from the patterned corelayer.

Said upper cladding layer is preferably provided on the core layer aftercuring the latter.

Said upper cladding layer can be provided using a known technique, forexample one of those listed in connection with the deposition of thecore layer and of the optional lower cladding layer on the support.

The second elastomeric material is preferably a curable siliconematerial, preferably having a lower refractive index than the refractiveindex of the core layer.

Preferably, when the second elastomeric material is a curable materialprovided in liquid form, a curing treatment thereof is effected. Forexample, the second elastomeric material can be cured by thermaltreatment or, preferably, by actinic radiation, for example UVradiation. Preferably, such UV curing is effected substantially in theabsence of oxygen, for example under a nitrogen flow, and preferably atroom temperature.

Preferably, the second elastomeric material is cured after beingprovided oil the core layer.

Preferably, the second elastomeric material is a polysyloxane having alower refractive index than the refractive index of the core layer.

Preferably, said second elastomeric material is an elastomeric materialselected from the group mentioned above in connection with theelastomeric material of the core layer.

Preferably, said first elastomeric material and said second elastomericmaterial both belong to a same class of materials. More preferably, saidelastomeric material of the core layer, as well as said first and secondelastomeric material all belong to the same class of materials.

Preferably, said first elastomeric material and said second elastomericmaterial have substantially equal refractive indexes.

Preferably, said first elastomeric material and said second elastomericmaterial are equal.

A further elastomeric material may be applied upon the upper claddinglayer. Such further elastomeric material can be added, for example, whenthe optical device comprises a plurality of optical waveguides providedin multilayer arrangement.

The method according to the present invention advantageously allows tomanufacture an optical device including at least one optical waveguidein a single step and in a reproducible manner.

The compatibility between the substantially rigid mold and the siliconelastomer to be patterned enables to obtain a patterned core layer withan improved surface smoothness with respect to that of the opticaldevices obtainable by the prior art methods based on thephotolithography technique, with a consequent reduction of the opticalloss, particularly of the scattering loss.

The method of the invention advantageously allows to produce a siliconeelastomer optical device having high dimensional and shape precision,which advantage is particularly important in the manufacture of rib andinverted rib waveguides, where a precise reproduction of the profile ofthe ribs is required in order to minimize the optical loss of theoptical device.

In addition to the improvement of the quality of the optical device, themethod of the invention also enjoys from the advantages deriving fromthe use of a substantially rigid mold, with advantageous reduction inthe number of steps and simplification thereof with respect to theetching technique of the prior art.

Furthermore, as described in more detail in the following, the method ofthe invention advantageously allows to obtain an optical device of thetype including a number of superimposed layers, namely a support, anoptional lower cladding, a core, and an upper cladding layer, whichstructure is particularly suitable in forming light guiding structures.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the invention will become morereadily apparent from the description of some preferred embodiments of amethod according to the invention for manufacturing an optical device,made hereafter with reference to the attached drawings in which, forillustrative and not limiting purposes, an optical device at differentmanufacturing steps of a preferred embodiment of the method of theinvention is represented.

In the drawings:

FIGS. 1-5 are cross-longitudinal views of an optical device beingmanufactured at subsequent steps of an embodiment of the method of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1-5, a sequence of manufacturing steps of anembodiment of the method of the invention for manufacturing anelastomeric optical device is schematically shown. In FIG. 5, showingthe final step of such preferred embodiment, a finished optical device,which will be described in greater detail in the following, is generallyindicated at 1. By way of illustrative example, in such figure anorganic rib optical waveguide is schematically shown.

In a first step of the method of the invention, a substantially rigidmold 2 having a predetermined pattern is provided. The mold 2 is shownin use in FIG. 2.

The substantially rigid mold 2, made for example of UV curablefluorinated acrylate (ZPU 13-430, manufactured by Zen Photonics Co.Ltd., Moonji-Dong, Yusong-Gu, Daejeon, South Korea), is provided with apredetermined recessed pattern intended to form the ribs of the riborganic optical waveguide.

The substantially rigid mold 2 is provided with recesses 3—correspondingto the ribs of the optical device 1—alternatively arranged betweenprojections 4, which are integrally formed with the substantially rigidmold 2 by way of a conventional technique as described in detail in thefollowing.

The substantially rigid mold 2 is formed by pouring the above-mentionedUV curable fluorinated acrylate in liquid form, on a master device (notshown as conventional per se), made for example of silicon, providedwith a pattern comprising projections corresponding to the recesses 3 ofthe mold 2, which pattern is obtained for example by a standardphotolithography technique. An inorganic support sheet, for example madeof quartz, not shown, is held horizontally by a conventional positioningdevice and leant by the same on the liquid. The mold is then UV cured bymeans of a Fusion D lamp (about 3 J/cm²) at room temperature. Thesubstantially rigid mold 2 is finally removed by peeling off from thesilicon master device and is ready to be used as mold for forming theoptical device 1.

According to an optional step of the present method, a support ofpolyetherimide (Ultem®, manufactured by Goodfellow Cambridge, ErmineBusiness Park, Huntingdon, England) shaped as a sheet, not shown in thefigures, may be provided.

According to a further optional step of the present method, a lowercladding layer 6 made, for example, of a thermally curable siliconeelastomer such as polydimethylsiloxane (PDMS) (for example Sylgard 184,refractive index=1.410, manufactured by Dow-Corning, Midland USA), isprovided in liquid form on the support, e.g. by spin-coating.

The lower cladding layer 6 is thermally cured at 150° C. for 15 min.

Subsequently, a core layer 7 of a thermally curable silicone elastomer,for example a polyphenylmethylsiloxane (for example OE 4100®, refractiveindex=1.460, manufactured by Dow-Corning, Midland, USA), of higherrefractive index with respect to the refractive index of the lowercladding layer 6 is provided in liquid form on the lower cladding layer6 (FIG. 1), e.g. by spin coating.

Subsequently, the core layer 7 is patterned by means of thesubstantially rigid mold 2 (FIG. 2), which can be guided against thecore layer 7 by a conventional positioning device. In such manner, thecore layer 7 is provided with a number of ribs 8 corresponding to therecesses 3 of the elastomeric mold 2. As schematically shown in FIG. 3,the core layer 7 is then thermally cured at 150° C. for 120 min.

The substantially rigid mold 2 is then removed by peeling off from thepatterned core layer 7 and may be re-used a number of times to pattern afurther core layer of a new optical device being formed.

Subsequently, according to a preferred embodiment of the present method,an upper cladding layer 9 of a thermally curable silicone elastomer,such as for example polydimethylsiloxane (PDMS) (for example Sylgard184, refractive index=1.410, manufactured by Dow-Corning, Midland, USA)of lower refractive index with respect to the refractive index of thecore layer 7, is provided in liquid form on the patterned core layer 7(FIG. 4), e.g. by spin coating.

The upper cladding layer 9 is then thermally cured at 150° C. for 15 min(FIG. 5).

In such manner, the finished optical device 1 including an elastomericrib optical waveguide comprising a core surrounded by a cladding havinga lower refractive index, is manufactured (FIG. 5).

Alternatively, according to the method of the invention an opticaldevice including a silicone elastomer inverted rib optical waveguidecomprising a core surrounded by a cladding having a lower refractiveindex, may be manufactured. In order to manufacture such a device of theinverted rib type, it is sufficient to pattern the lower cladding layer,forming a groove of the core layer dimensions. The groove is filled withthe core layer, defining also the outer rib height.

1-26. (canceled)
 27. A method for manufacturing an optical devicecomprising at least one silicone elastomer optical waveguide, comprisingthe steps of: providing a substantially rigid mold with a patternedsurface; providing a core layer made of a curable silicone elastomer;patterning said core layer by means of the patterned surface of thesubstantially rigid mold; curing the patterned core layer; and removingsaid substantially rigid mold from said patterned core layer.
 28. Themethod according to claim 27, wherein the core layer has an initialvolume and the cured patterned core layer has a final volume which issubstantially equal to said initial volume.
 29. The method according toclaim 28, wherein the final volume is 95-100% of the initial volume. 30.The method according to claim 27, wherein the core layer is made of athermally curable silicone elastomer.
 31. The method according to claim30, wherein the core layer is made of a material selected frompolyphenylmethylsiloxanes and polydimethylsiloxane.
 32. The methodaccording to claim 27, wherein the mold is made of a polymeric material.33. The method according to claim 32, wherein the mold is made of afluorinated polymeric material.
 34. The method according to claim 33,wherein the fluorinated polymeric material is selected from fluorinatedacrylate and methacrylate polymers, fluorinated polyacetates,fluorinated polyesters, fluorinated polystyrene, PVDF, fluorinatedpolycarbonates, fluorinated polyimides, fluorinatedpolyethyleneterephtalates, fluorinated polycyclobutanes, fluorinatedpolycyanates, or combinations thereof.
 35. The method according to claim34, wherein the fluorinated acrylate and methacrylate polymers areselected from fluorinated polymethylmethacrylate, fluorinatedpolybutylacrylate, fluorinated polyethylexylacrylate, fluorinatedpolyisodecylacrylate, fluorinated polyhydroxyethylacrylate, fluorinatedpolyhydroxypropylacrylate, fluorinated poycycloexylacrylate, fluorinatedpolybutane-dioldiacrylate, fluorinated polydiacrylate, fluorinatedpolyneopentylglycoldiacrylate, fluorinatedpolydiethylenegylcoldiacrylate, fluorinatedpolydiethyleneglycoldimethacrylate, and fluorinatedpolyexyanedioldiacrylate.
 36. The method according to claim 27, whereinthe mold is made of a material selected from: Si, Cr, Ni, Pt, and Ti.37. The method according to claim 36, further comprising the step ofapplying a releasing agent on the patterned surface of the mold beforesaid step of patterning the core layer.
 38. The method according toclaim 27, wherein the core layer is provided in direct contact with asupport.
 39. The method according to claim 38, wherein the support ismade of a material selected from: polyetherimide, polyimide,polycarbonate, polyurethane, quartz, and glass.
 40. The method accordingto claim 27, wherein the core layer is provided on a support providedwith a lower cladding layer of a first elastomeric material in contactwith the silicone elastomeric material of the core layer.
 41. The methodaccording to claim 40, wherein the lower cladding layer is made of afirst silicone elastomer in contact with the core layer.
 42. The methodaccording to claim 41, wherein the first silicone elastomer is a curablesilicone material having a lower refractive index than the refractiveindex of the core layer.
 43. The method according to claim 41, whereinthe first silicone elastomer is a polysiloxane having a lower refractiveindex than the refractive index of the core layer.
 44. The methodaccording to claim 41, wherein said first silicone elastomer is curedafter being provided on said support.
 45. The method according to claim27, further comprising the step of providing an upper cladding layer ofa second elastomeric material on the core layer after the step ofremoving the substantially rigid mold from the patterned core layer. 46.The method according to claim 45, wherein said upper cladding layer isprovided on the core layer after curing the latter.
 47. The methodaccording to claim 45, wherein the second elastomeric material is asecond silicone elastomer.
 48. The method according to claim 47, whereinthe second silicone elastomer is a curable silicone material having alower refractive index than the refractive index of the core layer. 49.The method according to claim 47, wherein the second silicone elastomeris a polysiloxane having a lower refractive index than the refractiveindex of the core layer.
 50. The method according to claim 47, whereinsaid second silicone elastomer is cured after being provided on saidcore layer.
 51. The method according to claim 40, wherein said firstsilicone elastomer and said second silicone elastomer have substantiallyequal refractive indexes.
 52. The method according to claim 47, whereinsaid first silicone elastomer and said second silicone elastomer havesubstantially equal refractive indexes.
 53. The method according toclaim 40, wherein said first silicone elastomer and said second siliconeelastomer are equal.
 54. The method according to claim 47, wherein saidfirst silicone elastomer and said second silicone elastomer are equal.